net: ibm: emac: Clear MAL descriptors without memset

Clear MAL descriptor rings with explicit field stores instead of
memset().  The descriptor rings are carved from MAL coherent DMA memory,
which may be mapped uncached on 32-bit powerpc.  The optimized memset()
path can use dcbz there and trigger an alignment warning.

Use WRITE_ONCE() for each field to prevent the compiler from merging
the stores back into a memset() call.

The skb tracking arrays remain ordinary CPU memory and still use memset().

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://patch.msgid.link/20260603230754.5535-1-rosenp@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/ibm/emac/core.c b/drivers/net/ethernet/ibm/emac/core.c
index d2194b406c9e11c88e0462b384af74e964bd6750..b7568d96aa47cc68f76c8eb7e8e5ec0326f9a736 100644 (file)
--- a/drivers/net/ethernet/ibm/emac/core.c
+++ b/drivers/net/ethernet/ibm/emac/core.c
@@ -1162,6 +1162,17 @@ static void emac_clean_rx_ring(struct emac_instance *dev)
        }
 }
 
+static void emac_clear_mal_desc(struct mal_descriptor *desc, int count)
+{
+       int i;
+
+       for (i = 0; i < count; i++) {
+               WRITE_ONCE(desc[i].ctrl, 0);
+               WRITE_ONCE(desc[i].data_len, 0);
+               WRITE_ONCE(desc[i].data_ptr, 0);
+       }
+}
+
 static int
 __emac_prepare_rx_skb(struct sk_buff *skb, struct emac_instance *dev, int slot)
 {
@@ -3089,8 +3100,8 @@ static int emac_probe(struct platform_device *ofdev)
        DBG(dev, "rx_desc %p" NL, dev->rx_desc);
 
        /* Clean rings */
-       memset(dev->tx_desc, 0, NUM_TX_BUFF * sizeof(struct mal_descriptor));
-       memset(dev->rx_desc, 0, NUM_RX_BUFF * sizeof(struct mal_descriptor));
+       emac_clear_mal_desc(dev->tx_desc, NUM_TX_BUFF);
+       emac_clear_mal_desc(dev->rx_desc, NUM_RX_BUFF);
        memset(dev->tx_skb, 0, NUM_TX_BUFF * sizeof(struct sk_buff *));
        memset(dev->rx_skb, 0, NUM_RX_BUFF * sizeof(struct sk_buff *));